1. The Field of the Invention
This invention relates to a warming device for shoes and in particular to a simple device for generating heat within a shoe during normal walking and running.
2. Brief Statement of the Prior Art
U.S. Pat. No. 3,534,391 discloses an electrical generator which is mounted on the outside of a ski boot which is driven from a tether that is connected between the generator and a ski. The generated current is passed through heating elements located in the ski boot. The external mounting and tether render this device quite cumbersome and difficult to use.
French Patent Nos. 7091,420 and 2365-973, and U.S. Pat. Nos. 4,507,877 and 3,977,093 disclose shoes with batteries mounted in the heels, and with electric resistance heaters in the soles of the shoes. Batteries require frequent replacement, and are particularly inefficient in a cold environment.
U.S. Pat. No. 1,506,282 discloses an electric generator mounted in a telescoping heel of a shoe which generates electricity for an electric lamp, heating coil, wireless outfit or a therapeutic appliance. A telescoping heel of this design would be very difficult to seal against water and mud, and the patented device would most likly be limited to indoor applications.
U.S. Pat. Nos. 2,442,026 and 1,272,931 disclose air pumps which are located in the heels of shoes and operated during walking. In the first mentioned patent, alcohol vapors are mixed with the air stream and passed over a catalyst to generate heat. In the latter patent, the air is forced through constricted passageways to generate heat by compression.
U.S. Pat. No. 382,681 discloses an armature which is mounted in a heel and manually rotated to generate heat by friction, which is dissipated in the shoe by metal conductors. U.S. Pat. No. 3,493,986 discloses an inner sole for a shoe which is formed of piezoelectric or magnetostrictive material which generate heat while the user walks.
U.S. Pat. No. 2,475,093 discloses a bouncing skate having spring coils on the bottom of its sole. German Patent Nos. 180866 and 620,963, and U.K. Patent No. 443,571 disclose springs mounted within a shoe for orthopedic purposes.
All of the aforementioned attempts to provide a self sustaining heater within a shoe have failed to recognize that there is relative movement between the wearer's heel and the heel of the shoe, or to harness this relative movement to generate heat. This relative movement can be sufficient, particularly when the wearer's weight is applied, to generate the necessary heat, provided a practical heat generator can be installed within the narrow confines of the shoe and heel, without significantly affecting its external appearance and comfort.